1. Field of the Invention
The present invention relates to a control system for detection of the failure of a lockup clutch in a vehicle having an engine capable of performing and stopping combustion in each cylinder group.
2. Description of the Related Art
A lockup clutch in an automatic transmission is usually engaged at a predetermined shift position for the purposes of improvement in fuel economy or the like. A method of controlling the slip amount of the lockup clutch according to an operating condition is generally adopted to absorb the shock due to complete engagement of the lockup clutch. For example, a target value for the slip amount of the lockup clutch in relation to the operating condition is preliminarily stored in a storage device according to a shift position, and the coupling capacity of the lockup clutch is controlled so that an actual slip amount becomes the target value.
Further known is an engine capable of performing and stopping combustion in each cylinder group for the purpose of improving fuel economy in particular. In such an engine, there is a difference in engine output torque characteristic between an all-cylinder operating condition and a partial-cylinder operating condition due to the difference in number of cylinders, and there is also a difference in engine output characteristic between the cylinder groups due to a minute difference in machining error or assembly error.
In a vehicle having such an engine capable of performing and stopping combustion in each cylinder group, it is necessary to prevent improper determination in determining the failure of a lockup clutch or a lockup clutch control device and to control the vehicle according to whether or not the failure has been detected.